1. Field of Invention
The invention relates to an improved heat sink and, in particular, to a heat sink with a heat dissipating base that has a three-dimensional curved surface.
2. Related Art
With the increasing efficiency of electronic devices, the heat dissipating device or system becomes indispensable equipment. If the heat produced by an electronic device is not released to the environment properly, the efficiency may deteriorate or the device may burn out. Therefore, the heat dissipating device is of particular importance to microelectronic devices (e.g. IC). With the increase in the density of elements and advance in the packaging technology, the IC's have even smaller areas. At the same time, the heat accumulated in each unit area grows. Therefore, highly efficient heat sinks always form an important research subject in the electronics industry.
Generally speaking, the heat dissipating device is installed on the surface of a heat-generating device to remove the heat form the device. According to the shape of the base, the heat dissipating devices can be categorized as planar and cylindrical ones.
Please refer to FIGS. 1, 2 and 3. FIG. 1 is a schematic view of the conventional heat 3 is a side view of the planar heat sink 20 along the 3—3 cross section. As shown in these drawings, the heat dissipating device 10 includes an axial-flow fan 12 and a planar heat sink 20. The planar heat sink 20 has a copper or copper alloy heat conductive plate 24, an aluminum or aluminum alloy heat dissipating shell 26 covering over the heat conductive plate 24, and a plurality of aluminum or aluminum alloy heat dissipating fins 22 perpendicularly installed on the heat dissipating shell 26. The fan 12 is embedded and fixed on the fins 22 of the heat sink 20. The lower surface of the heat conductive plate 24 is attached onto a heat-producing device (e.g. a CPU, not shown in the drawing).
The heat-producing device releases a lot of heat during operations. Since copper has an extremely good heat conductive property, the released heat rapidly flows toward the heat dissipating shell 26 and to the fins 22 through the heat conductive plate 24. The fan 12 further blows the heat on the fins 22 away, thereby achieving the heat dissipation effect. However, the produced heat forms a heat flow field (see FIG. 3) within the heat conductive plate 24. This results in a worse heat conductive effect in the central area of the base 24. Moreover, the position that generates the most heat in a typical heat-producing device is the central region. Therefore, the central area of the heat conductive plate 24 in the planar heat sink 20 requires a better heat conducting element to enhance the dissipation effect.
To improve the heat dissipation effect in the central region of the heat conductive plate 24, a cylindrical heat sink is proposed in the prior art. Please refer to FIGS. 4, 5 and 6. FIG. 4 shows another conventional heat dissipating device 30. FIG. 5 is a top view of the cylindrical heat sink 40 in FIG. 4. FIG. 6 is a side view of the cylindrical heat sink 40 along the 6—6 cross section. As shown in the drawings, the heat dissipating device 30 contains an axial-flow fan 12 (same as in FIG. 1) and a cylindrical heat sink 40. The cylindrical heat sink 40 is comprised of a copper or copper alloy heat conductive cylinder 44, an aluminum or aluminum alloy heat dissipating shell 46 covering over the rim of the heat conductive cylinder 44, and a plurality of aluminum or aluminum alloy fins 42 perpendicularly installed on the shell 46. Analogously, the fan 12 is embedded and fixed on the fins 42 of the heat sink 40. The other surface of the heat sink 40 is then attached onto the heat-producing device (e.g. CPU).
As the heat-producing device is in direct contact with the heat sink surface 40, the heat released during the operation of the heat-producing device quickly flows to the heat conductive cylinder 44, the heat dissipating shell 46, and the fins 42. Through the cylindrical design, the heat flows along the heat conductive cylinder 44, the shell 46, and the fins 42 in the axial direction toward to fan 12. The fan then provides air convection to bring out the heat.
From the above description, one sees that the cylindrical heat sink 40 indeed solves the unsatisfactory heat dissipation effect in the central region of the planar heat sink 20. However, it is easily seen from the heat flow field in FIG. 6 that the region close to the connection interface between the heat sink 40 and the fan 12 does not have a good dissipation effect. This obviously is a waste of available space in the heat dissipating device 30. It is very unpractical to use such devices in small electronics.
Furthermore, the heat conductive plate 24 of the heat sink 20 and the heat conductive cylinder 44 of the heat sink 40 are connected to the heat dissipating shell 26, 46 by soldering, bonding, or high-pressure mounting, respectively. If the precision of the heat conductive plate 24, he heat conductive cylinder 44, and the heat sinks 26, 46 is not high enough, air gaps may appear at the connection interfaces. Besides, soldering often increases the thermal resistance of the contact interface, also affecting the heat conduction effect of the heat sinks 20, 40.